Big Bang: Not Accelerating After All?

There are three reasons why we probably shouldn’t post this: (1) it’s off topic; (2) it’s loaded with math; and (3) it may be all wrong. Nevertheless, if it’s not wrong it’s important, so we’ll tell you what we know.

This is about some work by Dr. Arto Annila, a physics professor at the University of Helsinki. He’s written a paper, published in Monthly Notices of the Royal Astronomical Society, and available (at least the abstract) at the website of the Wiley Online Library. It’s titled Least-time paths of light. He says that the Universe is expanding uniformly — not at an increasing rate — and that all observations to the contrary can be explained without invoking dark energy and dark matter.

This is potentially of enormous importance, especially since the Nobel Prize in Physics for 2011 was recently awarded to Saul Perlmutter, Brian P. Schmidt, Adam G. Riess “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae.” According to the press release announcing the Prize:

The teams used a particular kind of supernova, called type Ia supernova. It is an explosion of an old compact star that is as heavy as the Sun but as small as the Earth. A single such supernova can emit as much light as a whole galaxy. All in all, the two research teams found over 50 distant supernovae whose light was weaker than expected – this was a sign that the expansion of the Universe was accelerating. The potential pitfalls had been numerous, and the scientists found reassurance in the fact that both groups had reached the same astonishing conclusion.

Now, just as we’ve all been getting used to the idea that the universe is expanding at an ever-increasing rate, and will probably never collapse in a Big Crunch, somehow resulting in another Big Bang — thus ending the idea of an eternally-oscillating universe — along comes Dr. Arto Annila with a different interpretation of the data. So we’re intrigued, even though we don’t pretend to follow all of the arguments.

The well-known problem resulting from these [Type 1a supernovae] observations is that this expansion seems to be occurring even faster than all known forms of energy could allow. While there is no shortage of proposed explanations – from dark energy to modified theories of gravity – it’s less common that someone questions the interpretation of the supernovae data itself.

In a new study, that’s what Arto Annila, Physics Professor at the University of Helsinki, is doing. The basis of his argument … lies in the ever-changing way that light travels through an ever-evolving universe.

[…]

“When the supernova exploded, its energy as photons began to disperse in the universe, which has, by the time we observe the flash, become larger and hence also more dilute,” he [Dr.Annila] said. “Accordingly, the observed intensity of light has fallen inversely proportional to the squared luminosity distance and directly proportional to the redshifted frequency. Due to these two factors, brightness vs. redshift is not one straight line on a log-log plot, but a curve.”

As a result, Annila argues that the supernovae data does not imply that the universe is undergoing an accelerating expansion.

We understood everything up to that last sentence. Let’s read on:

As Annila explains, when a ray of light travels from a distant star to an observer’s telescope, it travels along the path that takes the least amount of time. This well-known physics principle is called Fermat’s principle or the principle of least time. Importantly, the quickest path is not always the straight path.

[…]

The principle of least time is a specific form of the more generally stated principle of least action. According to this principle, light, like all forms of energy in motion, always travels on the path that maximizes its dispersal of energy. We see this concept when the light from a light bulb (or star) emanates outward in all available directions.

Okay. So far, so good. We continue:

Mathematically, the principle of least action has two different forms. Physicists almost always use the form that involves the so-called Lagrangian integrand, but Annila explains that this form can only determine paths within stationary surroundings. Since the expanding universe is an evolving system, he suggests that the original but less popular form, which was produced by the French mathematician Maupertuis, can more accurately determine the path of light from the distant supernovae.

Now we’re lost, and that seems to be right at the most important point. Here’s one more excerpt:

Using Maupertuis’ form of the principle of least action, Annila has calculated that the brightness of light from Type 1a supernovae after traveling many millions of light-years to Earth agrees well with observations of the known amount of energy in the universe, and doesn’t require dark energy or any other additional driving force.

He’s the first to think of this? Maybe so. We certainly didn’t think of it. Wait — we have to add this from the article:

Annila added that these concepts can be tested to see whether they are the correct way to analyze supernovae and interpret the universe’s expansion.

So there you are. There’s much more in the PhysOrg article, so of this interests you, click over there and check it out. Then let us know what you think. Hey, we’re talking about the fate of the universe!

9 responses to “Big Bang: Not Accelerating After All?”

He’s a physicist and writes very clearly and easy to understand for the layman… plus talking a lot about the expanding universe and dark matter. I think he actually has a post talking about this stuff. These might help: http://scienceblogs.com/startswithabang/dark-matter/

These kinds of analyses and cross-checks go on in physics all the time. It has been only recently – with the availability of the Internet – that the general public has been able to get a glimpse into this process.

And an interesting process it is. It is good that relatively straight-forward analyses get checked and rechecked, and that the theorists are constantly doing a double-take. As better data come in, and as more of the experts are drawn into the discussion of a particular set of findings, the more likely it is that the physics will be correctly ironed out.

That’s what makes it so much fun. Research at the frontiers is almost always like groping through a fog of incomplete data with large error bars and a number of theories that all can be made to fit until better measurements come along that can begin to distinguishing among them.

Curmy says, “It would be nice if this got resolved without dark energy. It always seemed like such a wildly ad hoc solution.”

Amen to that! Invoking dark energy made it seem to me that we really don’t know $h*t about the universe, but were just making up stuff to make it seem like we did. I wonder if someone will come along with a simple explanation for dark matter as well.

On the other hand, Lord Kelvin though he had it all figured out when he calculated the age of the Earth based on the rate of heat loss from the interior. Of course, he did this before anyone had any inkling of knowledge about radioactive decay, so he had no way of knowing that heat was constantly being generated inside the Earth. Since he made the assumption that all the heat of the Earth’s interior was residual from the Earth’s formation, his estimate of the Earth’s age was way short. In other words, he didn’t know *what* he didn’t know, and we may be in the same position vis-á-vis dark energy and dark matter.

It’s also humbling to recall that it’s been just a little more than a hundred years that we’ve known about radioactivity — and also radio waves, for that matter.

In the words of Jimmy Buffett regarding dark energy — “Maybe the Hokey-Pokey really is what it’s all about.”

I know a guy who proposes a 5-D manifold as a model for the universe; the fifth dimension is mass density. He says the 5-D math in his model accounts for the rotational speed of galaxies with no need to posit dark matter and for inflation of the universe with no need to posit dark energy.

Sounds wildly counter-intuitive to me, but then so did the 4-D manifold to everybody when Einstein made time a structural component of the universe rather than something separate.

Dr. Annila says the same evidence that causes us to posit dark matter can also be explained without it using his method.

This way of solving the dark matter issue is a bit more problematic. In this case, the rates of galactic rotation as a function of distance from galactic centers clearly indicate a distribution of dark matter surrounding galaxies. One can arrive at this conclusion using Newtonian physics alone. It’s a rather elementary calculation. Also, the distances from galactic centers are a very small percentage of the distances between galaxies and the size of the observable universe. So the expansion of the universe would be a much smaller effect on a local scale.

It doesn’t depend on light traveling over long periods of time in a universe that is expanding. That part of the picture cancels out in the measurements and calculations of the velocities of stars around a galactic center. And the velocity distribution of stars around the galactic center is different by a very large factor from what is expected if most of the mass of the galaxy were in the galactic center; it’s not a small effect.

One can look at the velocities of stars (as a function of distance from galactic center) on opposite sides of a galaxy and see symmetric Doppler shifts – down on one side, equally up on the other – and the effects of travel across space and time to telescopes on Earth are the same for both light paths. Both paths climb out of essentially the same gravitational potential well. So any effects due to the expansion of space-time are cancelled out.

I haven’t read the paper by Annila, but the method of Maupertuis comes from a time well before general relativity. In the Newtonian picture, time and space are separate and independent; but in relativity, time and space are intricately intertwined. This gives a different Doppler shift than what would be calculated if space and time were separate. In the use of the Type 1A supernovas, we are not comparing two light paths as we are in measuring galactic rotations.

Nevertheless, it is an interesting idea; and it is the kind of thing that goes on all the time. This is how our ideas get refined and honed for teaching new generations of physicists.

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